These days there exist radars with low probability of intercept, abbreviated LPI, which mostly use continuous or quasi-continuous transmission techniques, aiming to reduce the transmitted peak power.
These continuous transmission techniques, when they are employed alone, can be controlled by the implementation of modern detectors that use suitable processing operations that allow for a coherent integration of the signal over a long time, typically from one to several tens of ms.
Also, radars with continuous waves exhibit a major drawback, relating to the coupling between the transmission and the reception which are simultaneous, which tends to greatly limit their use when the required range is great, typically beyond one to several tens of km. A first problem to be resolved is therefore how to strengthen the “discretionary” nature of the radars in order for their detection to be as difficult as possible. A second problem is how to increase the range of the discreet radars.
Through their design, the abovementioned LPI radars are difficult to detect. These radars are conventionally radars with continuous waves, frequency modulation continuous wave (FMCW) or frequency shift keying (FSK) radars or even phase shift keying (PSK) radars or radars of Barker type that are known to those skilled in the art. The LPI radars are difficult to detect by conventional detectors which seek to detect a peak high power radar pulse. Moreover, the radars with continuous or quasi-continuous transmission are limited in range, because of the leaks between the transmitter and the receiver.
Hereinafter in the description, the expression “individual subarray” denotes an assembly consisting of several transmit or receive antenna elements. An antenna array or antenna consists of N individual transmitting subarrays or M receiving subarrays. The structure of the transmitting or receiving antennas or antenna array is of multiple input multiple output, or MIMO, type known to those skilled in the art. The individual subarrays can be identified in the antenna by an index.
The word “chirp” in this description describes a frequency ramp.